Technological and Biological Reliability, and Validity of Five Different CPET Systems During Simulated and Human Exercise

The validity and between-day reliability of cardiopulmonary exercise testing (CPET) systems remain largely unexplored. We therefore evaluate the validity and between-day technological and biological reliability of five popular CPET systems for assessing respiratory variables, substrate use, and energy expenditure during simulated and real human exercise. The following systems were assessed: Vyntus CPX, Oxycon Pro, VO2 Master, KORR, and Calibre. A metabolic simulator was used to simulate breath-by-breath gas exchange. The values measured by each system (minute ventilation (V?E), breathing frequency (BF), oxygen uptake (V?O<inf>2</inf>), carbon dioxide production (V?CO<inf>2</inf>), respiratory exchange ratio (RER), energy from carbohydrates and fats, and total energy expenditure) were compared to the simulated values to assess the validity. Six well-trained participants cycled 5% below their first ventilatory threshold on 2 days to verify the validity in human exercise. Between-session reliability was assessed in both the simulation and human experiments to determine technological and biological variability. Absolute percentage errors during the simulations ranged from 0.69% to 5.56% for V?E, 0.92% to 1.44% for BF, 3.12% to 7.86% for V?O<inf>2</inf>, 4.07% to 12.1% for V?CO<inf>2</inf>, 1.21% to 6.94% for RER, 2.83% to 48.8% for Kcal from carbohydrates, 14.1% to 50.3% for Kcal from fats, and 4.21% to 6.98% for total energy expenditure. Between-session variability during simulation (i.e., technological variability) ranged from 0.46% to 3.15% for V?O<inf>2</inf> and 0.71% to 4.99% for V?CO<inf>2</inf>. The error and between-day variability of the error for respiratory gas variables, substrate, and energy use differed substantially between systems. Biological and technological V?O<inf>2</inf> and V?CO<inf>2</inf> variability, respectively, accounted for ~60%–70% and 40%–30% of the variability in repeated human testing.